The first speed sensors began to be installed on cars with the advent of the fuel injection system. Over time, their design and principle of operation have changed several times. Modern sensors are based on the use of the Hall Effect - the appearance of a potential difference when a conductor with a constant current passes through a magnetic field. The practical application of this effect is that in one wheel revolution the sensor generates a certain number of pulses that are transmitted to the controller.

1. 850 (854)
2. 850 Estate (855)
3. 850 Rural (855)
4. S70 (874)
5. S70 Saloon (874)
6. V70 I (875, 876)
7. V70 � (875, 876)
8. C70 I Coupe (872)
9. C70 I Convertible (873)
10. V70 II (285)
11. V70 Mk II (285)
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The usage of the speed RPM sensor

Based on the number and the interval between pulses, the control unit calculates the vehicle speed, which is displayed on the instrument panel. The electronic control unit also uses the data received from the HOFFER brand Sensor, speed / RPM to adjust the engine operation in various speed modes. In most vehicles, the speed sensor is located on the gearbox near the output shaft. The impulse exciter is an annular multi-pole magnet fixed to the shaft. The most frequent breakdowns of the sensor are associated with a violation of the integrity of the electrical circuit, wire breaks or oxidation of contacts.